1. Field of the Invention
This invention relates to wireless communication and more particularly to systems and methods for increasing base station coverage and capacity in a wireless network, and even more particularly to such methods and systems for placement of wireless transceivers within a communication network.
2. Description of the Prior Art
One problem experienced in wireless communication systems is locating base stations. Once a base station (transmitter/receiver) is positioned in a coverage area it is important to be able to set its respective parameters in order to provided the desired coverage or capacity.
In this context, coverage is the geographical area covered by the signals to or from the base station while capacity relates to the amount of data that can pass through the base station to or from mobile devices. Base stations can be optimized for either coverage area or capacity (throughput). Typically, such optimization has been accomplished by using a sophisticated set of tools that are available to the wireless network designer. These tools would provide signal propagation models to the designer for use in calculating coverage areas for a particular base station. The designer would also estimate the interference that could result with respect to mobile devices communicating with a different base station some distance away, so these may or may not be on the same channel.
In some wireless networks the various base stations would use different channels or frequencies to avoid interference issues. Wireless network frequency planning is used to avoid, or minimize, such interference problems between adjacent and nearby base stations.
In newer wireless systems, such as, for example, orthogonal frequency-division multiplexing (OFDM) and orthogonal frequency-division multiple access (OFDMA), the tendency is to overlap frequencies and channels across base stations and to eliminate interference by assigning different combinations of sub-channels (sub-carriers) to different mobile devices communicating at the same time. These modulation schemes allow variable data rates and variable amounts of robustness in terms of being able to tolerate the interference. The ideal system is one in which a base station can serve a high number of mobile devices with no interference between devices. In order to achieve such an ideal system it is important that each communicating mobile device has a strong signal. If, on the other hand, there are two mobile devices each on the edge of coverage with two base stations and if propagation were uniform, those mobile devices would most likely experience interference. This interference would reduce the data rate for those devices in order to protect the integrity of the data.
Turning to the problem of location of a new transmitter/receiver (herein called a transceiver) the network designer, as discussed above, decides on a location, has the transceiver erected and installed and then tunes it up by adjusting the power level, the elevation angle of the antenna, etc. in accordance with the precalculated plan for this transceiver. Once these adjustments are made, the transceiver is turned on and “sees what actually happens.” The technician can then readjust the power levels, adjust the down tilt of the antenna, and possibly swap out the antenna with an antenna having a different azimuth angle. If the transceiver continues to cause interference, or not properly cover the designated area network, adjustments might have to be made, or the power level reduced further. In some instances the adjacent base stations also need to be read.